In many applications it is essential for a power supply to continue operating in the event power from the alternating current mains is interrupted. For that reason, battery back-up power supplies are known in which a battery is automatically switched into the power supply system to maintain the direct current output voltage of the system at least on a temporary basis, should the alternating current power be interrupted.
The present invention provides an improved, relatively simple and inexpensive battery back-up system which is constructed particularly for use in conjunction with an auxiliary channel of a converter type of switched power supply, and which incorporates circuitry for maintaining the battery in a charged condition during normal operation of the system, as well as built-in circuitry for protecting the battery and the system against excessive charge voltages and excessive power drain.
A feature of the invention is the provision of a fan which is operational during the normal mode and battery back-up mode of the system, to cool the power supply, and which is automatically turned off along with the auxiliary channel when the battery reaches a deep discharge condition, so as to protect the battery.